1. Field of the Invention
The present invention relates to methods for producing airtight containers, and in particular, relates to methods for producing vacuum-tight containers including electron-emitting elements thereinside.
2. Description of the Related Art
So-called field-emission displays (FEDs) including cold-cathode electron sources and phosphors capable of cathodoluminescence serving as image-forming members are well known. Vacuum-tight containers applicable to the FEDs need to maintain a constant high vacuum so as to maintain the electron-emission function for a long period of time. In order to maintain the vacuum in the vacuum-tight containers, the containers need to be hermetic. Thus, methods for producing airtight containers with high vacuum-tightness are required.
A method using frit glass as described in Japanese Patent Laid-Open No. 7-94102 (equivalent to European Patent Laid-Open No. 0609815) is well known as an example of a method for producing high-vacuum containers. An electron-source substrate with electron-emitting elements, a front substrate with a phosphor, and a frame member are joined to each other using frit glass, and the frit glass is fired so as to form an airtight container. Subsequently, the container is evacuated to a vacuum via an exhaust pipe connected to the airtight container. Finally, the exhaust pipe is chopped off, and the container is sealed. In this manner, production of a vacuum-tight container is completed.
However, the method described in Japanese Patent Laid-Open No. 7-94102 requires the temperature of the container to rise up to the softening and melting temperature of the frit glass during firing of the frit glass. This causes effects such as sublimation, oxidation, and reduction on electron sources on the electron-source substrate and the like in a marked manner, thereby causing variations in characteristics of the electron-emitting elements.
In order to mitigate the effects caused by the heating, a method in which an airtight container is disposed in a vacuum atmosphere throughout the production thereof, as described in Japanese Patent Laid-Open No. 2001-229828 (equivalent to European Patent Laid-Open No. 1126496), is well known. In this case, effects such as oxidation on electron-emitting elements can be suppressed by using a metal with a low melting point as a joining member. However, when high-definition and large-panel displays are required, there are issues such as accuracy in alignment during a bonding process in a high-temperature vacuum and cycle time for an evacuating process.
To resolve these issues, Japanese Patent Laid-Open No. 2000-149783 describes a sealing and bonding method using local heating by scanning high-density energy beams. This method includes alignment performed in an atmosphere of normal temperature and normal pressure and local heating. Therefore, thermal effects on electron-emitting elements are minimized, and a highly airtight and, at the same time, highly accurately aligned container can be produced at low cost. U.S. Pat. No. 6,722,937 and Japanese Patent Laid-Open No. 2000-313630 (equivalent to European Patent Laid-Open No. 0978489) also describe the joining methods using emission of high-density energy beams.
When joining members are softened and melted by scanning laser beams, the scanning speed also needs to be increased so that large-size or low-cost displays are produced. In this case, energy density of the laser source per unit time needs to be increased. However, some of the laser beams are reflected, and are not directly used for heating of the joining members. In addition, the reflected beams become stray light beams that may exert thermal effects on other members. In particular, when metal is used as a joining member so that more minute joining interfaces are obtained, the thermal effects of the stray light beams during the laser joining process may be enhanced due to the high reflectivity. When airtight containers are applied to FEDs and the like, it is not preferable in view of emission characteristics that the surface shapes and compositions of emitting portions of electron-emitting elements inside the FEDs vary.